The present invention relates to a foamed article of a chlorinated vinyl chloride resin (hereinafter referred to as "CPVC") containing inorganic materials, and more particularly to a foamed article of a CPVC containing inorganic materials having original characteristics of the CPVC that an obtained foamed article generates little heat, produces little smoke and is excellent in heat resistance and flame resistance, and the like and further, having a large dimensional stability defined by dimensional retention when an obtained foamed article is exposured in an atmosphere of high temperatures, for instance, the foamed article is left in the atmosphere of 200.degree. C. for one hour, which can be suitably used as heat insulating materials, building materials, chemical installation parts, electric equipments, vehicle parts, and the like.
The CPVC essentially shows flame resistance since the CPVC contains chlorine as one of the elements and the CPVC has the characteristics that an obtained foamed article generates little heat and produces little smoke when the article is compulsively burned.
Therefore, it has hitherto been expected that the foamed article of the CPVC is used as a heat insulating material having high fireproofing property.
However, the CPVC which is used as a base resin of a foamed article has problems that when the foamed article is heated to the temperature of 200.degree. C., the foamed article is rapidly shrunk and it can not be applied to a practical using and that when the foamed article is compulsively left in a burning atmosphere, the foamed article is shrunk to the stage which does not maintain its original shape.
Examples of conventional processes for preparing the foamed article of the CPVC are, for instance,
(1) a process for preparing a foamed article wherein a physical blowing agent is impregnated into a powder of the CPVC or a pellet of the CPVC and then the CPVC is extruded to carry out expansion with an extruder,
(2) a process for preparing a foamed article wherein a physical blowing agent is impregnated into a pellet and the pellet is introduced into a mold which is preheated to expand the pellet,
(3) a process for preparing a foamed article wherein the CPVC is introduced into an extruder, a physical blowing agent is introduced into the extruder under pressure and at the same time the CPVC and the physical blowing agent are melted and mixed together and then the melted CPVC mixture is extruded to carry out expansion,
(4) a process for preparing a foamed article wherein a CPVC is mixed with a chemical blowing agent and the CPVC is extruded to carry out expansion (however, the obtained foamed article is an article having a low expansion ratio, that is, about 3 times), and the like.
However, according to the conventional processes for preparing a foamed article of the CPVC, it is difficult to obtain a good foamed article containing a large amount of inorganic materials since cell membranes are broken when expanding and the obtained article has many opened cells even though a large amount of inorganic materials are contained in the CPVC.
In recent years, many studies of the process for preparing a foamed article have been investigated and, for instance, a process for preparing a foamed article of the CPVC wherein an alcohol is contained as a physical blowing agent in the CPVC and the CPVC is heated to expand, which is disclosed in Japanese Examined Patent Publication (Tokkyo Kokoku) No. 27300/1978 corresponding to U.S. Pat. No. 4,165,415; and a process for preparing a foamed article of the CPVC wherein a specific solvent is contained as a physical blowing agent in the CPVC and the CPVC is heated to expand, which is disclosed in Japanese Examined Patent Publication (Tokkyo Kokoku) No. 25340/1983 are well-known.
However, according to these processes, a foamed article of the CPVC having a required dimensional retention at high temperatures cannot be obtained.
The present inventors have studied to develop a foamed article having a suitable dimensional retention. As the results of their researches, according to the conventional processes, although cell membranes are broken at the time of expanding or the obtained foamed article becomes brittle when a large amount of inorganic materials are contained in the CPVC, they have found an unexpected foamed article having a suitable dimensional retention and not having the above-mentioned problems and the process for preparing thereof by including a large amount of inorganic materials into the CPVC and they have accomplished the present invention.